β-glucocerebrosidase is a soluble lysosomal enzyme that functions at the luminal membrane surface through interactions with Saposin C and anionic phospholipids to hydrolyze the glycolipid glucosylceramide. β-glucocerebrosidase is particularly important in tissue macrophages to break down and recycle membranes from engulfed damaged cells and pathogens. Since glucosylceramide is the primary precursor molecule for more than 300 glycolipids and gangliosides that are involved in numerous important cellular pathways and signaling cascades, it is essential to maintain the intricate balance for these various lipid molecules.
Gaucher disease is caused by a deficiency in β-glucocerebrosidase that results in the accumulation of glucosylceramide. Gaucher disease manifests itself through various clinical symptoms including anemia, thrombocytopenia, hepatosplenomegaly and skeletal abnormalities. Gaucher disease is classified in three categories based on neurological involvement: type 1 (non-neuronopathic); type 2 (acute neuronopathic); and type 3 (chronic neuronopathic). There is no known cure for Gaucher disease, but enzyme replacement therapy (ERT), which supplements the deficient β-glucocerebrosidase and substrate reduction therapy which inhibits the synthesis of glucosylceramide are approved treatments for this disease. Other therapeutic approaches such as small molecule pharmacological chaperones and protein folding modulators are also being evaluated as potential treatments of this disease. Of these treatment approaches, ERT is the most established and effective clinical treatment for the visceral symptoms of Gaucher disease. Imiglucerase (recombinant β-glucocerebrosidase; Cerezyme™, Genzyme Corp.™) was developed and approved by the FDA in 1994 for the treatment of Gaucher disease and is currently the standard of care for this disease.
While Cerezyme™ ERT is widely considered to be the most effective treatment, this lysosomal enzyme is not stable at neutral pH and 37° C. In fact, the vast majority of the drug is irreversibly inactivated in blood shortly after intravenous infusion. Only the small fraction that retains catalytic activity and is internalized into the target macrophages confers the entire therapeutic effect. Hence, it would be advantageous to develop a more stable β-glucocerebrosidase enzyme that is not as susceptible to enzyme inactivation from the protein production step through physiological conditions that would be encountered upon introduction into a human subject in need thereof.